Moldvay/Cook shortly after its release.
Some of the friends who started playing with me picked up the Mentzer copy in the 1983-1984 time frame. I don't think we noted any compatibility issues or rules changes if there were any. We just presumed all changes were cosmetic and kept playing basicly as we had been.
My group moved by steps into AD&D sometime probably around 1985, adopting the Players Handbook first because of the race/class combinations, then the Monster Manual for its expanded monster lists, and then the DMG by stages as we came to understand the rules. Was pretty fully AD&D by 1987 or so, and by 1989 I was using alot of obscure rules that weren't widely adopted (Weapon vs. Armor modifiers, for example).
Changed group about then. Continued to play 1e through about 1995 with slow adoption of some of the 2e rules (Bards, Dragons, probably a few other things) while still using the 1e books as the primary reference. Quit D&D for GURPS due to growing frustration with some of the limitations and inconsistancies of the rules and came back again about 2001. Now playing 3.0 in a modified form with some changes ported from 3.5 and will likely to do so for the foreseeable future.